The present invention relates to a tool for cutting solid material, said tool comprising a tool body and a cutting insert of cemented carbide, said cutting insert being secured to the tool body by brazing. The invention also relates to a cutting insert per se.
When a tool according to the present invention is cutting a relatively hard, solid material, e.g., sandstone, the cutting insert will be subjected to very high forces, said forces creating a turning moment that gives rise to tensile stresses in certain portions of the surface of the cutting tip. Also the turning moment will eventually be transformed to the brazed joint.
Cutting inserts of cemented carbide that are subjected to high bending stresses must have a high toughness, i.e., lower hardness compared to cutting inserts that are subjected basically to compressive stresses. In mineral and asphalt cutting, lateral forces are present to a relatively high degree. Therefore, cutting inserts of the type having a relatively low hardness and high Co-content are chosen for mineral and asphalt cutting. A high Co-content is also favorable in reducing brazing stresses.
The wear resistance of a cutting insert as described above consequently is low and in no way optimal as regards length of life. It is therefore common to choose big cutting inserts having a big volume of cemented carbide for mineral and asphalt cutting. By way of such an arrangement, one can handle the bending stresses and the tool also gets an acceptable length of life.
In conventional tools for mineral and asphalt cutting, the big volume cutting inserts are properly embedded in the tool blank made out of steel. Such an arrangement makes sure that the cutting insert is not subjected to too high stresses.
However, such a design means that the steel of the blank surrounding the cutting insert quite soon gets in contact with the mineral or asphalt that is worked. Especially when minerals are worked, the contact between minerals and steel will initiate sparking that can be very dangerous, e.g., in mines having inflammable gases. Contact between a cutting insert of cemented carbide and minerals will normally not initiate sparking.
Since the cemented carbide cutting insert for cutting mineral and asphalt has a relatively big volume, the tool itself is also voluminous. This means that very powerful machines are needed to carry the tools.
As mentioned above, the turning moment acting upon the cutting insert will be transferred to the brazed joint. A conventional brazed joint between the cutting insert and the tool body has normally a substantially constant thickness. This means that only a peripheral part of the brazed joint will be active in absorbing the turning moment.
Especially in mineral cutting one speaks of technically cuttable material and economically cuttable material. The technically cuttable material is the hardest material that can be worked by a cutting action. The economically cuttable material is the hardest material that can be worked by cutting action in economic superiority to other methods.